1. Field of the Invention
The invention relates generally to a communications system that communicates data over a narrow or limited bandwidth medium. More particularly, the invention relates to a method and apparatus for transmission of video over narrow-band transmission channels, such as plain old telephone service (POTS) lines.
2. Description of the Related Art
Video telephones have existed within the marketplace for several years with limited commercial success. The lack of success of videophones is attributable in part to the fact that they do not work very well. It has been problematic to transmit sound and video of acceptable quality across existing telephone lines.
Some available video conferencing systems produce acceptable video and audio quality, and have met with some commercial success. These video conferencing systems depend on wide bandwidth communication connections such as leased lines, ISDN (Integrated Services Digital Network), DSL (Digital Subscriber Lines) and the like. The high bandwidth is necessary to produce acceptable audio and video quality.
The available bandwidth on standard telephone lines has been too low to support industry standard 30 frames per second video. Currently, using compression, the best performance obtainable on standard U.S. telephone lines is approximately 15 video frames per second in one direction. Because 15 video frames per second is less than the persistence of the human eye, which is generally about 24 frames per second, the 15 video frames per second results in a jerky unacceptable video quality. Even with expensive compression hardware, the quality of the resultant video may be unacceptable.
There is therefore a need for video communications systems, which do not depend on expensive compression hardware and yet yield an acceptable video display when transmitted bi-directionally across standard analog telephone lines.